Stent island removal system

ABSTRACT

A tool, system, and method for removing islands from a stent is disclosed. The tool includes a tube with at least one exit hole in communication with the interior of the tube, and the tube being connected to a pressurized fluid source. A stent island is located over the exit hole and is removed by the force of the exiting fluid from the exit hole.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 11/825,985 which was filed on Jul. 9, 2007, now U.S. Pat. No.7,823,263 B2 which claims the benefit of U.S. Patent Application No.60/830,208 which was filed on Jul. 11, 2006, both of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to implantable medical devices, such as stents.

2. Description of the State of the Art

A typical stent is a cylindrically shaped device, which holds open andsometimes expands a segment of a blood vessel or other anatomical lumensuch as urinary tracts and bile ducts. Stents are often used in thetreatment of atherosclerotic stenosis in blood vessels. “Stenosis”refers to a narrowing or constriction of the diameter of a bodilypassage or orifice. In such treatments, stents reinforce body vesselsand prevent restenosis following angioplasty. “Restenosis” refers to thereoccurrence of stenosis in a blood vessel or heart valve after it hasbeen subjected to angioplasty or valvuloplasty.

Stents have been made of many materials including metals and polymers.Polymer materials include both nonbioerodable and bioerodable plasticmaterials. In some applications, a polymeric bioerodable stent may bemore advantageous than a metal stent due to its biodegradeability andgreater flexibility relative to the metal stent.

The cylindrical structure of a stent is typically composed of ascaffolding that includes a pattern or network of interconnectingstructural elements or struts. The scaffolding can be formed from wires,tubes, or planar films of material rolled into a cylindrical shape.Furthermore, the pattern that makes up the stent allows the stent to beradially expandable and longitudinally flexible. Longitudinalflexibility facilitates delivery of the stent and rigidity allows astent to hold open a lumen of a tubular organ. Generally, the patternshould be designed to maintain the longitudinal flexibility and rigidityrequired of the stent. The stent should also have adequate strength inthe circumferential direction.

A number of techniques have been suggested for the fabrication ofmetallic and polymeric stents from tubes and planar films or sheets.Examples of such techniques include laser cutting or etching a patternonto a material. Laser cutting may be performed on a planar film of amaterial which is then rolled into a tubular configuration.Alternatively, a desired pattern may be etched directly onto a tube.Other techniques involve cutting a desired pattern into a sheet or atube via chemical etching or electrical discharge machining Lasercutting of stents has been described in a number of publicationsincluding U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005to Richter, and U.S. Pat. No. 5,906,759 to Richter.

Additionally, a polymeric wire may be coiled to form a polymeric stent.In yet another method, a polymeric stent may be formed from a tube bylaser cutting a pattern of cylindrical rings and connecting rings in thetube itself. See, e.g., U.S. Pat. No. 6,585,755 to Jackson et al.

“Islands” refer to pieces or portions of metal or polymeric tubingmaterial that are not intended to be part of a stent pattern, and thatremain attached to stent struts after laser cutting. The pieces orportions may have a relatively weak physical attachment to a strut ormay be wedged between struts with no physical attachment to the struts.Stent islands are conventionally removed from the stent by inserting ametal mandrel through the stent and tapping the mandrel against asurface. This method of removing stent islands after laser cutting thestent causes vibrations that essentially shake the islands out of thestent. However, such vibrations may also damage the stent. Inparticular, regions of a stent that are exposed to high stress duringstent use may be damaged, which may weaken the stent in these highstress regions.

Additionally, a medicated stent may be fabricated by coating the surfaceof either a metallic or polymeric scaffolding with a polymeric carrierthat includes an active or bioactive agent or drug. Polymericscaffolding may also serve as a carrier of an active agent or drug.

Furthermore, it may be desirable for a stent to be biodegradable. Inmany treatment applications, the presence of a stent in a body may benecessary for a limited period of time until its intended function of,for example, maintaining vascular patency and/or drug delivery isaccomplished. Therefore, stents fabricated from biodegradable,bioabsorbable, and/or bioerodable materials such as bioabsorbablepolymers should be configured to completely erode only after theclinical need for them has ended.

SUMMARY OF THE INVENTION

Various embodiments of the present invention include a system forremoving stent islands from a laser cut tube comprising: a tubeincluding at least one hole having an opening in an outer surface thatis in fluid communication with an interior of the tube; a stentpositioned over the tube, wherein the stent comprises a scaffoldingincluding a pattern of interconnecting struts formed by laser cuttingthe pattern into a second tube, wherein the stent comprises a stentisland, the island being pieces or portions of material of the secondtube that are not intended to be part of the pattern that remainattached to the struts of the stent after the laser cutting; and a highpressure gas source connected to the tube to supply a compressed gas tothe interior of the tube, wherein when the high pressure gas sourcesupplies the compressed gas to the interior of the tube, the compressedgas exits the tube through the at least one hole and facilitates removalof the island.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a stent.

FIG. 2 depicts a stent island removal tool according to an embodiment ofthe invention.

FIGS. 3A-C depict hole patterns according to various embodiments of theinvention.

FIGS. 4A-B depict a stent island removal tool according to an embodimentof the invention.

FIGS. 5A-C depict hole opening patterns according to various embodimentsof the invention.

FIGS. 6A-E depict the profiles of holes according to various embodimentsof the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a stent 10 that includes a number of interconnectingstructural elements or struts 11. In general, the pattern of the stentstruts is designed so that stent 10 can be radially compressed andexpanded. Stent 10 may include portions of struts that are straight orrelatively straight, an example being a straight portion designated byreference numeral 12. Stent 10 may also include portions of struts thatare bent, such as the portions designated by reference numerals 13, 14,and 15. Bent portions 13, 14, and 15 may bend further when stent 10 iscrimped radially inwardly. Bent portions 13, 14, and 15 may bend furtheroutward when stent 10 is expanded radially outwardly. In someembodiments, a stent such as stent 10 may be fabricated by laser cuttinga strut pattern on a tube. In other embodiments, chemical etching may beused to form a strut pattern on a tube.

FIG. 1 depicts exemplary stent islands 16 and 17 formed after lasercutting the stent into a pattern or chemically etching the pattern.Island 16 has a relatively weak physical attachment to a strut 18 andisland 17 is wedged between struts 19 and 20. Due to the relatively weakattachment, the invention provides a method and an apparatus forremoving such islands by blowing a gas stream at or near the islands.The apparatus and method are designed to consistently remove stentislands through the use of a pressurized fluid such as a gas. The use ofpressurized fluids minimizes any damage to the stent.

Embodiments of the present invention include a tube with at least onehole or opening that is adapted to receive a stent thereon. In someembodiments, a stent having islands is mounted over the tube and a fluidconveyed through or into the tube flows out of the hole. The stent withislands is mounted or positioned on the tube hole such that the conveyedfluid flowing through the hole facilitates removal of an island.

One embodiment of a stent island removal tool 100 is shown in FIG. 2.Tool 100 is composed of a tube 110 with an outer diameter that is thesame or larger than the inner diameter of a stent 120 that is positionedover tube 110. In certain embodiments, stent 120 has a slip fit, meaningstent 120 is slidably mounted to allow axial and rotational movement.One end 130 of the tube may be occluded and the other end 135 isconnected to a high-pressure fluid source 140. In another embodiment,both ends of tube 130, 135 may be occluded, and the pressurized fluid140 would enter from the surface of the tube (not shown). One or moreopenings 150 are located on the surface of tube 110 to allow thecompressed fluid to exit openings 150. In one embodiment, openings 150are located at other circumferential positions of tube 110. Thecompressed fluid blows radially through openings 150, blowing theislands off stent 120.

In certain embodiments, stent 120 may be mounted on tube 110 using aninterference fit or press fit. In such an embodiment, the outer diameterof tube 110 is the same or substantially the same as the inner diameterof stent 120. The fit is tight enough that the stent does not slideaxially or rotate during stent removal.

In several embodiments where stent 120 is slidably mounted, islands invarious portions of the stent may be removed by translating the stentaxially, as depicted by arrow 160, rotationally as depicted by arrow170, or both, to remove islands in the various portions of the stent. Inother embodiments, tube 110 may be moved axially or rotationally withrespect to stent 120 such that the at least one hole may remove islandsin various portions of the stent. In further embodiments, both stent 120and tube 110 are moved with respect to each other. In one embodiment,the relative rotational movement of the stent and tube can be providedby attaching the tube to a fixture that rotates the tube. In anotherembodiment, relative axial movement of the stent and tube can beprovided by attaching the tube to a fixture that vibrateslongitudinally. Such a fixture can also rotate the stent to provide bothrelative rotational and translational motion.

In several embodiments, a tube 300 for removing stent islands may havemore than one opening 350, as illustrated in FIGS. 3A-C. The openingsmay be arranged in different patterns such as circular patterns (3A),longitudinal patterns (3B), or helical (3A), but the patterns are notlimited thereto.

In some embodiments, stent island removal can be performed with littleor no relative movement of the stent with respect to the stent islandremoval tube. FIGS. 4A-B are an illustration of a stationary stentisland removal procedure. Holes in tube 410 are not shown for the sakeof clarity. Alternatively or additionally, stent 420 has an interferencefit with tube 410 such that the stent remains stationary on the tubewhile the blowing occurs. In some embodiments, rotational and axialmovement of stent 420 may be reduced or prevented on tube 410 withcollets 450, at the ends of stent 420. Alternatively, only one collet450 may be used around one end of stent 410 if the other end of thestent is pressed against a stationary portion of the tool. In oneembodiment, tube 410 has a sufficient number of holes such that all ormost of the islands on the stent are removed. FIG. 4B depicts tube 410showing a high density of holes 460. In other embodiments, the holes arein a pattern coincident with the likely location of stent islands for agiven stent pattern. Different stent patterns may require different tubehole patterns.

The force of the fluid through the holes should be large enough toremove a stent island. Force depends on the flow rate of the fluidconveyed into the tube, and the pressure of the fluid in the tube. If acompressible fluid, such as a gas is used, then the temperature of thegas is an additional factor in determining the force out of the tube.The force of the gas should not be high enough such that it causesdamage to the stent. Because the islands may vary in size, differentsized holes may be necessary. The size of the holes should be determinedrelative to the islands and width of the struts. In several embodiments,the size of the holes is determined such that the force per unit areaapplied on the islands is high enough to remove the island, but not sohigh as to damage the surrounding struts. If the hole is smaller, then ahigher force may be necessary to remove the islands.

The method of removing stent islands can include multiple passes of thestent over the gas flowing from the opening(s). The gas flow the flowcan be continuous, variable, or pulsed by controlling the gas supply.Continuous flow is a constant flow over time. A variable flow is achanging flow over time. A pulsed flow is an on-off type of flow, andmay be continuous or variable. The pulses may occur at regularintervals, or irregular intervals.

The gas velocity, the gas flow direction, the gas temperature, the gaspulse frequency, etc. can be varied to provide a force needed to removethe stent islands. Various types of gases may be used in the presentinvention, including but not limited to air, argon, oxygen, nitrogen,carbon dioxide.

In one embodiment, the tube is cooled to make the stent islands morebrittle so they may be removed more easily. In another, the gas may becooled, further cooling the islands. In a further embodiment, both thetube and the gas may be cooled.

It is also contemplated that the cross-section of the openings can havea variety of shapes. In some embodiments, the shape of the opening canbe circular, oval, square, or rectangular. In particular embodiments,the openings may be slits. FIGS. 5A-C depict various arrangements ofslits in a tube. FIG. 5A depicts a tube 550 with a pattern of slits 510arranged axially, with the major axis of the slits 510 aligned with thelongitudinal axis. FIG. 5B depicts a tube 551 with a pattern of slits511 arranged circumferentially, with the major axis of the slits 511aligned around the circumference of the tube. FIG. 5C depicts a tube 552with a pattern of slits 512 arranged helically, with the major axis ofthe slits 512 aligned at an angle to the longitudinal axis. Using alonger rectangular slit may allow the fluid to exit as a thin sheetrather than a point flow of fluid through a circular opening.

The size of the cross-section of the holes between the inside andoutside of the tube can be constant or can vary. FIG. 6A depicts a tube600 with a hole 650 with a constant cross-section. FIG. 6B-C depicttubes 610 and 620 with holes 651 and 652 having cross-sections thatincrease and decrease, respectively. Hole 651 acts to disperse fluidflow, while hole 652 acts to concentrate fluid flow.

In further embodiments, the holes can be adapted to direct airflow in aselected direction. FIGS. 6D-E depict tubes 630 and 640 with holes 653and 654 that direct fluid flow at an acute angle to the surface of thetubes.

In several embodiments, the tube is made of metal. In other embodiments,the tube may be made of a polymeric material. The selection of materialmay be based on operating temperature, pressure, duty cycle,compatibility of the tube material with the stent material or gas, cost,but is not limited thereto. In some embodiments, the tube is stainlesssteel.

The present invention removes stent islands while maintaining stentintegrity. The method and apparatus of the invention can be used toremove metal or polymeric stent islands from stents. Examples of stentsfor use in the invention include, without limitation, self-expandablestents, balloon-expandable stents, stent-grafts, and vascular grafts.

Polymers for use in fabricating a substrate of a stent or a coating fora stent can be biostable, bioabsorbable, biodegradable or bioerodable.Biostable refers to polymers that are not biodegradable. The termsbiodegradable, bioabsorbable, and bioerodable are used interchangeablyand refer to polymers that are capable of being completely degradedand/or eroded when exposed to bodily fluids such as blood and can begradually resorbed, absorbed, and/or eliminated by the body. Theprocesses of breaking down and eventual absorption and elimination ofthe polymer can be caused by, for example, hydrolysis, metabolicprocesses, bulk or surface erosion, and the like.

It is understood that after the process of degradation, erosion,absorption, and/or resorption has been completed, no part of the stentwill remain or in the case of coating applications on a biostablescaffolding, no polymer will remain on the device. In some embodiments,very negligible traces or residue may be left behind. For stents madefrom a biodegradable polymer, the stent is intended to remain in thebody for a duration of time until its intended function of, for example,maintaining vascular patency and/or drug delivery is accomplished.

The underlying structure or substrate of a stent can be completely or atleast in part made from a biodegradable polymer or combination ofbiodegradable polymers, a biostable polymer or combination of biostablepolymers, or a combination of biodegradable and biostable polymers.Additionally, a polymer-based coating for a surface of a device can be abiodegradable polymer or combination of biodegradable polymers, abiostable polymer or combination of biostable polymers, or a combinationof biodegradable and biostable polymers.

Representative examples of polymers that may be used to fabricate orcoat an stent include, but are not limited to, poly(N-acetylglucosamine)(Chitin), Chitosan, poly(hydroxyvalerate), poly(lactide-co-glycolide),poly(hydroxybutyrate), poly(hydroxybutyrate-co-valerate),polyorthoester, polyanhydride, poly(glycolic acid), poly(glycolide),poly(L-lactic acid), poly(L-lactide), poly(D,L-lactic acid),poly(D,L-lactide), poly(caprolactone), poly(trimethylene carbonate),polyester amide, poly(glycolic acid-co-trimethylene carbonate),co-poly(ether-esters) (e.g. PEO/PLA), polyphosphazenes, biomolecules(such as fibrin, fibrinogen, cellulose, starch, collagen and hyaluronicacid), polyurethanes, silicones, polyesters, polyolefins,polyisobutylene and ethylene-alphaolefin copolymers, acrylic polymersand copolymers other than polyacrylates, vinyl halide polymers andcopolymers (such as polyvinyl chloride), polyvinyl ethers (such aspolyvinyl methyl ether), polyvinylidene halides (such as polyvinylidenechloride), polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics(such as polystyrene), polyvinyl esters (such as polyvinyl acetate),acrylonitrile-styrene copolymers, ABS resins, polyamides (such as Nylon66 and polycaprolactam), polycarbonates, polyoxymethylenes, polyimides,polyethers, polyurethanes, rayon, rayon-triacetate, cellulose, celluloseacetate, cellulose butyrate, cellulose acetate butyrate, cellophane,cellulose nitrate, cellulose propionate, cellulose ethers, andcarboxymethyl cellulose. Another type of polymer based on poly(lacticacid) that can be used includes graft copolymers, and block copolymers,such as AB block-copolymers (“diblock-copolymers”) or ABAblock-copolymers (“triblock-copolymers”), or mixtures thereof.

Additional representative examples of polymers that may be especiallywell suited for use in fabricating or coating an implantable medicaldevice include ethylene vinyl alcohol copolymer (commonly known by thegeneric name EVOH or by the trade name EVAL), poly(butyl methacrylate),poly(vinylidene fluoride-co-hexafluororpropene) (e.g., SOLEF 21508,available from Solvay Solexis PVDF, Thorofare, N.J.), polyvinylidenefluoride (otherwise known as KYNAR, available from ATOFINA Chemicals,Philadelphia, Pa.), ethylene-vinyl acetate copolymers, and polyethyleneglycol.

A non-polymer substrate of the stent may be made of a metallic materialor an alloy such as, but not limited to, cobalt chromium alloy(ELGILOY), stainless steel (316L), high nitrogen stainless steel, e.g.,BIODUR 108, cobalt chrome alloy L-605, “MP35N,” “MP20N,” ELASTINITE(Nitinol), tantalum, nickel-titanium alloy, platinum-iridium alloy,gold, magnesium, or combinations thereof “MP35N” and “MP20N” are tradenames for alloys of cobalt, nickel, chromium and molybdenum availablefrom Standard Press Steel Co., Jenkintown, Pa. “MP35N” consists of 35%cobalt, 35% nickel, 20% chromium, and 10% molybdenum. “MP20N” consistsof 50% cobalt, 20% nickel, 20% chromium, and 10% molybdenum.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications can be made without departing from thisinvention in its broader aspects. Therefore, the appended claims are toencompass within their scope all such changes and modifications as fallwithin the true spirit and scope of this invention.

1. A system for removing stent islands from a laser cut tube comprising:a tube including at least one hole having an opening in an outer surfacethat is in fluid communication with an interior of the tube; a stentpositioned over the tube, wherein the stent comprises a scaffoldingincluding a pattern of interconnecting struts formed by laser cuttingthe pattern into a second tube, wherein the stent comprises a stentisland, the island being pieces or portions of material of the secondtube that are not intended to be part of the pattern that remainattached to the struts of the stent after the laser cutting; and a highpressure gas source connected to the tube to supply a compressed gas tothe interior of the tube, wherein when the high pressure gas sourcesupplies the compressed gas to the interior of the tube, the compressedgas exits the tube through the at least one hole and facilitates removalof the island.
 2. The system of claim 1, further comprising at least onecollet securing the stent to the tube.
 3. The system of claim 1, whereinthe stent is positioned over the tube with a slip fit that allows foraxial and rotational movement of the stent.
 4. The system of claim 1,wherein the tube has an outer diameter the same as the inner diameter ofthe stent.
 5. The system of claim 1, wherein one end of the tube isoccluded and the other end is connected to the high pressure gas source.6. The system of claim 1, wherein each end of the tube is occluded andthe high pressure gas source is in fluid communication with the interiorof the tube through the surface of the tube.
 7. The system of claim 1,wherein the tube is attached to a fixture that rotates the tube.
 8. Thesystem of claim 1, wherein the holes are arranged in a circumferentialpattern around the circumference of the tube.
 9. The system of claim 1,wherein the holes are arranged in a helical pattern around the tube. 10.The system of claim 1, wherein the holes are arranged in a pattern alongthe longitudinal axis of the stent.
 11. The system of claim 1, whereinthe cross-section of the holes between the inside and outside of thetube increases so that the hole acts to disperse gas flow.
 12. Thesystem of claim 1, wherein the cross-section of the holes between theinside and outside of the tube decreases so that the hole acts toconcentrate gas flow.
 13. The system of claim 1, wherein the scaffoldingis made of a bioabsorbable polymer.
 14. The system of claim 1, whereinthe island is positioned over the hole.